Method of treating molten metals



Patented Feb. 26, i946 UNITED STATES PATENT OFFICE 2,395,458 METHOD OF TREATING MOLTEN METALS Arthur T. Cape, Columbus, Ohio, assig-nor to Coast Metals, Inc., Canton, Ohio, a corporation of Delaware No Drawing. 1 Application February 28, 1 945, Serial No. 580,271

14 Claims.

It has been found imposssible, however, to pass such gas through a molten mass of metal in suificient quantities to either produce the high state of ebullition which can be produced by the use of solid carbon dioxide (Dry Ice), or to provide a sufiicient reaction of the CO2 for the removal of gases such as hydrogen from the metal.

It has also been proposed, as in Patent No. 2,008,731, to place Dry Ice on ,the surface of a and causing the container to be submerged below the surface of the molten metal to be treated. In this case, however, precautions must be taken to insure that the container is not air-tight, else a violent explosion might occur.

(e) Placing the Dry Ice in the bottom of a mold into which the molten metal to be treated is Poured for making castings, etc., care being taken that the mold is of such designthat the gaseous CO2 which is formed may be eliminated freely.

In all of the foregoing cases, the Dry Ice i so introduced into or associated with the molten metal to be treated that a substantial or violent ebullition of the molten metal occurs, due to the magnitude of the volume change of the Dr Ice from the solid to the gaseous state. The reaction is of such violence that the gases in the-molten molten charge of aluminum, prior to the addition of magnesium and similar readily oxidizable metals thereto, in order to provide a dry protective atmosphere above the aluminum to prevent buming of the added metals. The use of Dry Ice in this manner does not, however, produce any appreciable ebullition of the molten metal, nor is it effective to any appreciable degree in degasifying the molten metal.

I have discovered, however, that I can produce a. violent ebullition of the molten metals, particularly molten metals, containing appreciable amounts of at least one of the metals of the group consisting of nickel, cobalt, iron,.chromium, tungsten and molybdenum, a ubstantially complete degasification of such metals, and a desired metallographic structure of the metals, by introducing or associating the solid carbon dioxide or Dry Ice with the molten metals in various ways which have'not been suggested or contemplated in the aforesaid patents. Among these are the following:

(a) Placing the Dry Ice, in amounts of from about 20 to about 1000 ounces per ton of molten metal to be treated, in the bottom of the ladle to be filled with the metal to be treated and pouring the molten metal thereover.

(b) Placing the Dry Ice in the bottom of the forehearth, and then pouring the molten metal thereover.

(c) Placing the Dry Ice in the runner leading from the furnac to the ladle or forehearth and then "flowing thereover the molten metal to be treated.

(d) Placing the Dry Ice in a metallic container metal, particularly hydrogen, are completely and effectively removed.

It is important, moreover, particularly in the manufacture of steel, that the Dry Ice be used as near towards the end of the refining period as possible, but prior to the addition of deoxidizing agents, such as silicon, aluminum, calcium, zirconium, etc. The reason for this is that these socalled deoxidizin agents have a tendency to hold various gases in solution, so that the effectiveness of the Dry Ice treatment i partially lost if the Dry Ice is used after the addition of the deoxidizing agents. On the other hand, if the deoxidizing agents are added after the use of theDry Ice, then any overoxidization which may have taken place is immediately corrected. but the detrimental gases, such as hydrogen, will have been eliminated.

I have found that the use of solid carbon dioxide or Dry Ice in the manner described is particularly effective in connection with the manufacture of high alloy castings, particularly nickelor cobalt-containing castings of small size, where internal porosity is often found. By the use of Dry Ice in the various ways which have been described, such internal porosity is eliminated and a tougher, finer and denser-appearing structure is obtained.

The treatment which has been described has been found of especial value for ferrous-base alloys, for nickel-base alloys such as those described in my co-pending applications, Serial Nos. 519,889 and 543,047, for alloys of the nichrome and stellite types, and for cobalt-chromium-tungsten alloys which are relatively iron-free.

This application is a continuation-in-part of my co-pending application, Serial No. 533,393,

1. The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel, cobalt, iron, chromium, tungsten and molybdenum, which comprises treating the metal with solid carbon dioxide in such a manner as to cause substantial ebullition of the metal.

2. The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel,

cobalt, iron, chromium, tungsten and molybdenum, which comprises treating the metal with solid carbon dioxide in such a manner as to cause a violent ebullition of said metal.

3. The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel, cobalt, iron, chromium, tungsten and molybdenum, which comprises treating the metal with solid carbon dioxide, the latter being disposed within and below the surface of the metal throughout said treatment.

4. The method of degasiiying molten metal containing at least one of the-metals of the group consisting of nickel, cobalt, iron, chromium,tungsten and molybdenum, which comprises flowing the molten metal over solid carbon dioxide.

5. The method of degasifying molten metal containing at least oneof the metals of the group consisting of nickel, cobalt, iron, chromium, tungsten and molybdenum, which comprises placing solid carbon dioxide in amounts of from about 20 to about 1000 ounces per ton of molten metal to be degasified, in the bottom of a ladle to be filled with said metal, and pouring the molten metal thereover. 1

6. The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel, cobalt, iron, chromium, tungsten and molybdenum, which comprises placing solid carbon dioxide, in small amounts, in the bottom of a forehearth to be filled with said metal, and pouring the molten metal into said forehearth.

7. The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel, cobalt, iron, chromium, tungsten and molybdenum,'which comprises plac ins solid carbon dioxide in the runner leadms ,which was allowed January 1'1, 1945, but has from a. furnace to a ladle or forehearth, and then flowing thereover the molten metal to be degasifled.

8. The method 0'! degasifying molten metal containing at least one of the metals of the group mnsisting cf nickel, cebalt, iron, chromium, tungsten and molybdenum, which comprises causing a non-air-tight container which contains solid carbon dioxide to be submerged below the surface of the molten metal to be degasified, the container being so maintained until degasiflcation is substantially complete.

9.'The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel, cobalt, iron, chromium,

tungsten and molybdenum, which comprises placing solid carbon dioxide in the bottom of a mold. and pouring the molten metal which is to be cast in said mold into said mold and over said carbon dioxide.

10. The method of degasifying molten metal containing at least one of the metals of the group consisting of nickel, cobalt, iron, chromium, tungsten and molybdenum, which comprises treating the molten metal with solid carbon dioxide in such a manner as to cause a substantial 12. The method of eliminating internal porosity from ferrous base castings, and obtaining a tougher, finer and denser-appearing structure therein, which comprises treating the molten metal from which said castings are to be made with solid carbon dioxide in such a manner as to cause substantial ebullition of said metal.

13. The method of degasifying ferrous base metals while in molten condition, which comprises bringing solid carbon dioxide into such association with the molten metal as to cause h violent ebullition of the latter.

14. The method of improving the structure of ferrous base castings which comprises bringing solid carbon dioxide into such association with the molten metal from which th castings are to be made as to cause violent ebullition of said metal and a removal of the gases therefrom.

- ARTHUR T. CAPE. 

